I just put in a crate 4.6L engine in my 98 with 185K miles. The truck sat for four months while I was taking my time doing the work. During this time I drained the tranny and changed the filter. When I eventually got around to starting it (BTW - it started on the 1st try), after I let it run for about 10 minutes, I engaged the transmission. No go - either in drive or reverse. I shut it down. No reading on the tranny dipstick. Added 2 quarts of Mercon V, cranked it up - I've got motion now! Drove it around the neighborhood, noticed when going from park to drive, you have to wait a couple of seconds for it to engage - also happens in reverse. Checked tranny fluid again - this time while it was running. Fluid still low. Added another 1 1/2 quarts - now it reads on the dipstick (no leaks!, just not enough fluid initially). So, I know my fluid level is fine. Truck runs very good and it shifts great when driving, I just don't know what the deal is with having to wait for it to engage in either drive or reverse. Any transmission gurus out there?

 

Not a guru but wanted to say don't panic yet. I had a tranny rebuilt and had the same problem took it to the guy he adjusted something and it got better but never went away drove it for another 6 months before I got a new truck no issues.

Something needs adjusting and one of the guru's will tell you what